Reuters/Carlo Allegri

Geographic and genetic reasons why you're sneezing more after a move.

Dear CityLab: I recently moved to a new city, and almost as soon as I arrived, I started experiencing seasonal allergy symptoms. Am I allergic to my new city?

Yes and no. Allergists say it typically takes two to five years to become sensitized to an allergen, and the clock starts ticking from the point of exposure, which means the flora of your previous city might share the blame.

Let's say, for instance, that you're allergic to ragweed but never had seasonal allergy symptoms back at your old place. It's still possible that you were exposed to ragweed pollen in the other city; it's one of the most prevalent and potent allergens in the U.S. A single ragweed plant can produce 1 billion granules of pollen in a season, and even if there isn't one near you, the pollen can travel up to 400 miles. Chances are you breathed it in at some point.

When you were exposed to ragweed, your body produced an antibody called Immunoglobulin E (IgE) in response. This antibody is specific to ragweed and trained to recognize granules when they enter your system. Now, anytime you breathe in ragweed, IgE kicks your immune system into overdrive. The antibodies bind to mast cells in the skin, eyes, nose, throat, and lungs, and release inflammatory "mediators," such as histamine, that cause sneezing, sniffling, nasal congestion, itchy eyes, and other classic allergy symptoms. In other words, you are now sensitized to ragweed.

But this process, from exposure to sensitization, can take years. That was the case for allergist Susan Raschal, who didn't experience hay fever until she moved from Chicago to Chattanooga. Raschal tested positive for ragweed allergy back when she lived in Chicago, but pollen levels there were never high enough to produce a reaction. Chattanooga, by comparison, has a much more robust pollen season—it's #14 on this year's list of Spring Allergy Capitalsand the city's valley location traps pollen and other pollutants to create a perfect storm for allergy sufferers.

Those other airborne irritants add another wrinkle to the "I'm allergic to my city" narrative: Your symptoms might be caused by a sensitivity to environmental factors like pollution, weather, and barometric pressure changes—not an allergy per se. Those irritants can induce allergy-like symptoms even though you are not, strictly speaking, "allergic" to them.

Moving to a new place is hard enough without sneezing fits. (Shutterstock/Image Point Fr)

You must be immunologically programmed to have an allergy (that is, the IgE antibody must be involved), but you can be sensitive to just about anything—diesel exhaust, cigarette smoke, potpourri. The only way to know what's really causing your symptoms is to ask your doctor to perform an allergy test.

The trees around your new home and your old one are partly responsible for your symptoms this time of year—and you can't just move again to escape them. In the 1950s, Americans headed to the Southwest seeking allergy relief in the desert. But now cities like Tucson and Las Vegas are just as miserable as the rest of the country, appearing near the top of the Allergy Capitals list year after year. That's because people brought non-native plants—allergic triggers—with them, increasing the pollen load in Tucson by tenfold in just two decades. If you're looking to avoid allergies entirely, Raschal has some chilling advice for you: "Where you need to go is Alaska."

Top photo: Reuters/Carlo Allegri

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